When an audio signal is compressed or transmitted, an audio signal of some frequency bands may be lossily compressed or transmitted for efficient compression or transmission. The audio signal where data of some frequency bands is lossy may have a deteriorated sound quality or tone, compared to an audio signal before the loss.
Therefore, in order for an audio signal including a lossy frequency band to be reproduced close to an original sound with a high sound quality, it is required to effectively reconstruct an audio signal of the lossy frequency band.